1. Field of the Invention
The present invention relates to an object, a method, or a manufacturing method. In addition, the present invention relates to a process, a machine, manufacture, and a composition of matter. One embodiment of the present invention particularly relates to a semiconductor device, a display device, a light-emitting device, a driving method thereof, and a manufacturing method thereof. One embodiment of the present invention particularly relates to a light-emitting element, a display module, a lighting module, a display device, a light-emitting device, an electronic device, and a lighting device in which an organic compound is used as a light-emitting substance.
2. Description of the Related Art
In recent years, research and development of a light-emitting element (organic EL element) which uses an organic compound and utilizes electroluminescence (EL) have been actively promoted. In the basic structure of such a light-emitting element, an organic compound layer containing a light-emitting substance (an EL layer) is provided between a pair of electrodes. By voltage application to this element, light emission from the light-emitting substance can be obtained.
Since such a light-emitting element is of self-light-emitting type, it is considered that the light-emitting element has advantages over a liquid crystal display, such as high visibility of pixels and no need of backlight, and is therefore suitable as a flat panel display element. A display including such a light-emitting element is also highly advantageous in that it can be thin and lightweight. Besides, very high speed response is one of the features of such an element.
Furthermore, an organic EL element can provide planar light emission. Thus, a large-area element can be easily formed. This feature is difficult to obtain with point light sources typified by incandescent lamps and LEDs or linear light sources typified by fluorescent lamps. Thus, the light-emitting element also has great potential as a planar light source which can be applied to a lighting device and the like.
A display or a lighting device including an organic EL element having such features is applied to a variety of electronic devices and used in a variety of environments. For example, a display of an in-vehicle navigation system or the like is constantly located in a car; a dashboard of a sun-heated car in summer often reaches a temperature as high as or higher than 80° C. Since the above-described light-emitting element is formed by stacking layers of a variety of organic compounds, it may deteriorate and become inoperative when placed in a high temperature environment.
There is a demand for a highly heat resistant light-emitting element with reduced deterioration of characteristics even after it is placed in a high temperature environment as described above (see Patent Documents 1, for example).